Digging near a shared boundary fence is one of those jobs that looks straightforward but can quickly become complicated. Done carelessly, it can undermine fence posts, damage underground services, or even cause a fence to collapse — creating both a safety hazard and a neighbourly dispute. Follow these steps to do it safely and correctly.
Talk to Your Neighbour First
Before you pick up a spade, have a conversation with your neighbour. Under the Fencing Act 1978, a boundary fence is generally a shared asset, meaning both parties have rights and responsibilities regarding it. If your excavation could affect the fence's stability or footings, your neighbour has a legitimate interest in knowing about it. A quick, friendly chat can prevent misunderstandings and potential legal headaches later. Document any agreement in writing — even a simple text message trail helps.
Check for Underground Services
This is the most critical safety step. Striking a buried power cable, gas line, or water pipe can be fatal or cause serious damage. Before any digging, you must locate all underground services in the area.
- Contact Dial Before You Dig (0800 248 344 or online at beforeudig.co.nz) to request a service location. This is a free service and is considered standard practice on any excavation job in NZ.
- Your local council may also hold records of stormwater and wastewater pipes near your boundary.
- Be aware that older properties may have services that aren't accurately mapped — treat any unmarked area with caution.
- Once services are marked, hand-dig carefully within 500 mm of any marked line before using mechanical equipment.
For electrical safety guidance, refer to WorkSafe NZ, which provides clear information on excavation hazards including buried cables.
Understand the Soil and Fence Footing Depth
Before digging, assess what you're working with:
- Fence post depth: Standard timber fence posts in NZ are typically set 600–900 mm into the ground. Excavating close to these footings can loosen or destabilise them.
- Soil type: Clay soils can shift and crack when disturbed; sandy or loose soils can collapse quickly. If you're unsure of your soil conditions, consult a geotechnical professional.
- Trench depth and shoring: Any trench deeper than 1.5 metres requires proper shoring or battering (sloping the sides) to prevent collapse under WorkSafe NZ excavation guidelines. Note that a trench is not automatically classified as a "confined space" — confined space is a specific legal term with its own requirements; check with WorkSafe NZ if you believe your excavation may also meet that definition.
How Close Can You Dig?
As a general rule of thumb used in the trade:
| Fence post size | Recommended minimum clearance |
|---|---|
| Light timber post (100×100 mm) | At least 300–500 mm from post base |
| Heavy timber or concrete post | At least 500–700 mm from post base |
| Retaining wall or block fence | Consult a structural engineer |
These are guides only — the actual safe distance depends on soil conditions, footing depth, and what you're digging for. When in doubt, dig by hand and go slowly.
Do You Need a Building Consent?
This depends on what you're digging for. Many minor excavations for garden beds or drainage are exempt from consent under Schedule 1 of the Building Act 2004, but deeper excavations, retaining walls over 1.5 metres, or work near the boundary may require consent. Always check with your local council before starting — rules vary by region and site. You can find general guidance at MBIE Building Performance.
If you're installing or replacing the fence itself as part of the project, note that fencing work is generally not restricted building work, but structural retaining walls may be.
Safe Digging Techniques
- Mark out your dig zone with spray paint or pegs before starting.
- Hand-dig first in the area closest to the fence and any marked services.
- Keep spoil (excavated soil) away from the fence line — piling it against posts adds load and can cause leaning.
- Work in stages rather than opening a long trench all at once.
- Never undercut the soil beneath fence footings.
- If using a mechanical excavator, ensure the operator is experienced and aware of all service locations and the proximity of the fence.
Restricted and Licensed Work
If your excavation involves connecting to or working near gas pipes, electrical cables, or plumbing/drainage, be aware of NZ's restricted work rules:
- Electrical work near or on cables must be carried out by a registered electrician. See EWRB for licensing requirements.
- Gas work is restricted to licensed gasfitters registered with the PGDB.
- Plumbing and drainlaying connections are also restricted — check the PGDB for what homeowners can and cannot do.
Safety note: If you strike an underground service while digging, stop immediately. For a gas leak, evacuate the area and call your gas network operator and 111. For a damaged power cable, do not touch it — call your lines company and 111.
When to Call a Professional
Hire a qualified excavator operator or civil contractor if:
- The dig is deeper than 1 metre, especially near the boundary
- You're working in unstable, wet, or clay-heavy soils
- The fence is a retaining wall or masonry structure
- You're unsure about underground service locations
- The project requires a building consent
A professional excavator will carry the right equipment, insurance, and experience to protect both your property and your neighbour's. You can find qualified local excavation contractors on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
